Method for matching a particle filter temperature adjustment

ABSTRACT

The invention relates to a method for adjusting the temperature of a particle filter of an exhaust line ( 1 ) during a regeneration phase of said filter by injecting fuel into the exhaust gases, and which includes the steps of: measuring the temperature (T 5 ) in the particle filter; predetermining an amount of fuel to inject into the exhaust gases (Qigec), said amount including a first component (Qd c) predetermined by means of an open control loop not factoring in the measured temperature, and said amount including a second component (Qc 2 ) predetermined by means of a closed control loop factoring in the measured temperature; and, on the basis of the amplitude of the second component relative to the predetermined fuel amount, predetermining a correction term (Kc) of the first component and applying said correction term in the open control loop.

The present invention claims the priority of French application 0855119 filed on Jul. 25, 2008, the content of which (text, drawings and claims) is incorporated here by reference.

The invention relates to particle filters, and in particular methods for regulating the temperature of a particle filter associated with a system of diesel fuel injection in the exhaust.

A widely known technique for reducing the exhaust gas particle content of a diesel engine consists in using a filter to capture these particles as they exit the engine.

The particles accumulate in the filter and form soot, which must be treated to avoid clogging of the filter. This treatment takes place by raising the temperature of the filter in order to burn the accumulated soot.

In order to implement this treatment in an optimum manner, a first approach consists of adding an additive to the fuel in order to lower the combustion temperature of the soot from 600° C. to 450° C.

According to a second approach, diesel fuel is injected directly into the exhaust gas. The combustion of this diesel fuel inside an oxidizing catalyst upstream of the filter heats the exhaust gas and brings the filter to the required temperature of 600° C. This temperature must be regulated in order to keep the temperature as stable as possible, and to ensure rapid and effective regeneration.

The application with registration number FR07 57789 in name of the applicant describes a method for regulating the temperature at the entrance of the filter. This method associates an open loop and a closed loop in order to regulate the temperature of the gas at the entrance of the particle filter and to ensure combustion of the soot. The open loop and the closed loop determine the respective components of a quantity of fuel to be injected into the exhaust. The quantity of fuel to be injected in the exhaust is determined by accumulation of these components.

This type of regulation has however some inconveniences. In practice, the exhaust elements to be regulated are subject to aging, in particular the catalyst, the different temperature probes, the air flow meter and the fuel injector. Leaks in the fuel circuit can also occur. The production of the exhaust also leads to dispersions. Since the thermal efficiency of the catalyst deteriorates with aging, a larger quantity of fuel will have to be injected into the exhaust to ensure regeneration. In normal operation, the closed loop compensates this lack of fuel. Because of the thermal energy of the exhaust circuit, the closed loop correction produces its effects with a certain delay. To ensure nevertheless that the temperature remains within the desired temperature range, one solution can consist of lengthening the regeneration phases, to the detriment of engine operation. Otherwise, these variations of the regulation can result in too high a temperature being applied at the entrance of the catalyst, which can lead to its destruction.

The goal of the invention is to resolve one or more of these inconveniences. The invention relates also to a method for adapting the temperature regulation of a particle filter in an exhaust line during a regeneration phase of this filter, by injecting fuel into the exhaust gas, comprising the steps consisting of measuring the temperature of the particle filter, determining the quantity of fuel to be injected into the exhaust gas, this quantity comprising a first component determined through the intermediary of an open control loop not taking into account the measured temperature, and this quantity comprising a second component determined through the intermediary of a closed control loop taking into account the measured temperature and, as a function of the amplitude of the second component in comparison with the determined quantity of fuel, determining a corrective factor for the first component and applying this corrective factor in the open control loop.

According to a variant, the method comprises the calculation of an indicator representing the amplitude of the second component in comparison with the quantity of injected fuel, and application of the correction factor of the first component in the open control loop when the indicator exceeds a predetermined threshold.

According to another variant, the threshold is calculated as a function of at least one operating parameter of the engine.

According to another variant, the correction factor of the first component is only applied in the open control loop when several successively calculated values of the indicator exceed said threshold.

According to another variant, said indicator I is calculated with the following equation:

$I{\square\frac{\int_{RG}^{\;}{\left( {\frac{{Qc}\; 2}{{{{Qc}\; 2}}{\square Q_{IGEC}}}{\square\frac{{Qc}\; 2_{ini}}{{{{Qc}\; 2}}_{ini}{\square Q_{{IGEC}_{ini}}}}}} \right)\ {t}}}{\int_{RG}^{\;}{t}}}$

where RG is the regeneration time, Q_(c2ini) and Q_(c2) are the flow values of the second component calculated respectively at a reference time and during the calculation in progress, Q_(igecini) and Q_(igec) are the flow values of the quantity of fuel to be injected in the exhaust gas calculated respectively at a reference time and during the calculation in progress.

According to another variant, the open control loop is based on a model estimating the temperature at the particle filter as a function of the exhaust gas flow, the exhaust gas temperature upstream of the oxidizing catalyst which is installed upstream of the particle filter, and as a function of the quantity of fuel to be injected into the exhaust gas.

According to a variant, the method comprises the detection of an engine dysfunction and maintenance of the applied correction factor when a dysfunction is detected.

According to another variant, the closed control loop comprises an integral proportional regulator.

The invention relates also to an automotive vehicle equipped with an exhaust line comprising a particle filter, comprising a fuel injection device in the exhaust line upstream of the particle filter; a device for measuring the temperature at the particle filter; and a device for determining the quantity of fuel to be injected into the exhaust gas in order to regulate the temperature of the particle filter, and comprising an open control loop that does not take into account the measured temperature and calculating a first component of said fuel quantity, and comprising a closed control loop that takes into account the measured temperature and calculating a second component of said fuel quantity.

The device for determining the quantity of fuel to be injected calculates a correction factor for the first component and applies this correction factor in the open control loop as a function of the amplitude of the second component in comparison with the calculated quantity of fuel to be injected.

Other characteristics and advantages of the invention will become clear from the following description, provided as non-limiting example, with reference to the attached drawings, in which:

FIG. 1 illustrates schematically an exhaust line in which the invention is implemented;

FIG. 2 illustrates an example of the method for regulating the regeneration temperature of the particle filter;

FIG. 3 illustrates schematically the method for applying a correction factor to the amplitude of the open loop.

The invention proposes to modify the respective amplitudes of the two components of a quantity of fuel to be injected into the exhaust. The amplitude of a component determined by a closed control loop taking into account the temperature of the particle filter is modified as a function of a component determined by an open control loop not taking into account this temperature.

FIG. 1 illustrates a diesel engine 9 comprising an exhaust line 1. The exhaust line 1 comprises an exhaust collector 2. The exhaust gas passes through collector 2 at a temperature T4, measured by temperature probe 7, and has a flow Qair, typically measured by a flow meter (not shown). The exhaust line comprises a diesel fuel injector 3. Injector 3 is installed upstream of an oxidizing catalyst 4. Catalyst 4 is installed upstream of a particle filter 5. During regeneration, the temperature T5 of the air entering particle filter 5 must be maintained at approximately 600° C. to allow for the combustion of soot formed by the captured particles. To this end, diesel fuel is injected into the exhaust through the intermediary of injector 3. The injected fuel is oxidized by catalyst 4 during an exothermic reaction. A temperature probe 6 measures the temperature at the particle filter 5, typically in a junction conduit between the oxidizing catalyst 4 and the particle filter 5.

A control device 8 illustrated in FIG. 2 commands the fuel injections by injector 3 in order to regulate the temperature T5 at the particle filter 5 during a regeneration. The temperature probe 6 measures the exhaust gas temperature T5 at the entrance of particle filter 5. This temperature T5 must not be too high—which would provoke deterioration or premature aging of filter and catalyst—nor too low—which would stop soot combustion and increase the overall regeneration time of the filter. The air temperature T5 at the entrance of filter 5 is known thanks to probe 6. The target temperature to be achieved varies based on the location of this probe 6, because the temperature inside filter 5 is higher than at its periphery.

Control device 8 determines a quantity of fuel to be injected into the exhaust gas. This quantity is determined in the form of a fuel flow command Q_(igec) of injector 3 during an injection time. A flow command associated with an injection time constitutes in this way a fuel quantity command. The flow of fuel to be injected is determined by two components, Qc1 c and Qc2. The sum of these two components is equivalent to the value of the flow command Q_(igec).

The first component Qc1 c is determined through the intermediary of an open control loop. This open control loop does not take into account temperature T5 measured by probe 6. The open control loop is intended to have a rapid response time. Advantageously, the open control loop is intended to define more than 85 to 90% of the amplitude of the calculated fuel quantity to be injected.

The open control loop uses for instance a thermal behavior model of catalyst 4, as a function of the flow of the diesel fuel injector Q_(igec), the exhaust gas temperature T4 and the exhaust gas flow upstream of catalyst 4. A calculation module 83 is used for this purpose, which exploits the thermal behavior model of catalyst 4 to calculate an estimate of the temperature T5 at particle filter 5.

The thermal behavior of catalyst 4 depends on rapid regulation parameters such as the air flow in collector 2 of the exhaust line 1. In fact, homogenization of the temperatures in this line 1 occurs more rapidly with higher air flow. A second rapid regulation parameter is the temperature T4 of the exhaust gas at the entrance 2 of the exhaust line 1. A significant increase of this temperature T4 generated by engine 9 results in an increase of the temperature at the entrance of catalyst 4. Analogously, this temperature rise at the entrance of the catalyst causes a rise of the temperature T5 of filter 5—minus the heat loss to the exterior. Besides these rapid regulation parameters, there are slow regulation parameters of the filter temperature which the heat propagation characteristics inside the catalyst influence the temperature T5 at the filter.

The know-how of the technology indicates that, in a first approximation, the hydrocarbon concentration inside catalyst 4 generates the rise of the temperature T5. This concentration is defined by the relationship between fuel flow and air flow and can be taken into account in the model.

The calculation module 83 issues a flow command Qc1 as a function of this model.

The second component Qc2 is determined through the intermediary of a closed control loop. The closed control loop takes into account the temperature T5 measured by probe 6. This temperature T5 is compared to a temperature command Ct. The temperature command Ct is for instance 600° C. The difference between T5 and Ct is applied at the entrance of an integral proportional regulator 81. The regulator 81 determines the second flow component Qc2 as a function of the error corresponding with this difference. The regulator 81 determines the second component Qc2 by taking into account a factor in proportion with the difference and a factor integrating this difference. The objective of the integral factor is to ensure that temperature T5 is as close as possible to temperature command Ct.

Control device 8 comprises a correction device 84. This correction device 84 determines the amplitude of the second component Qc2 in comparison with the fuel flow Q_(igec). As a function of this amplitude, correction device 84 determines a correction factor Kc to be applied to the first component. This correction factor is then applied in the closed control loop. Correction factor Kc is a multiplication factor for flow command Qc1, so that Qc1 c=Qc1*Kc. It can also be envisaged that the correction factor is added to the command Qc1.

By correcting the amplitude of the first component generated by the open loop, the temperature regulation at the particle filter will not be affected by aging of the exhaust line components 1, clogging of the fuel dosage element (for instance the metering pump or the injector), drifting of temperature probes 6 and 7 or drifting of the air flow meters. Indeed, the proportion of the first component in the injected fuel quantity command must be maintained, so that the aging of the components will not induce an accrued preponderance of the second component calculated by the closed loop. In this way, the regulation will not be affected by increased delay of its correction and the duration of the regeneration phase can be maintained. In addition, the risk of destroying catalyst 4 due to transient excessive exhaust gas temperature is also reduced because the amplitude of the second component is limited by the correction of the first component.

The correction device 84 typically increases the value of correction factor Kc when the amplitude of the second component Qc2 increases in comparison with the injected fuel quantity Q_(igec).

To validate the application of correction factor Kc in the first component Qc1 c, device 84 calculates an indicator I representative of the amplitude of the second component Qc2 in comparison with the injected fuel quantity Q_(igec). The calculated correction factor Kc is only applied when indicator I exceeds a predetermined threshold. The calculated correction factor Kc replaces then the value of the previously applied correction factor. The threshold for validating the application of the new correction factor Kc can be calculated as a function of the operating parameters of the engine such as vehicle speed, engine torque or engine speed. In this way, the adaptation conditions of the first component will depend on the driving pattern of the vehicle.

The untimely application of the new correction factor can be avoided during transient operating conditions. To further reduce the risk of untimely change in correction factor, the condition can be established that the indicator exceeds said threshold several times in succession prior to validating the application of the new calculated correction factor Kc. Indeed, since aging or drifting of the components is a slow phenomenon, it is desirable that new correction factors are not applied at too short intervals.

Advantageously, to avoid that an engine dysfunction, for instance an internal or external fuel leak, would lead to erroneous application of correction factor Kc, the application of the current correction factor is maintained when such dysfunction is detected.

The indicator I can be calculated with the following equation:

$I = \frac{\int_{RG}^{\;}{\left( {\frac{{Qc}\; 2}{{{{Qc}\; 2}} + Q_{IGEC}} - \frac{{Qc}\; 2_{ini}}{{{{Qc}\; 2}}_{ini} + Q_{{IGEC}_{ini}}}} \right)\ {t}}}{\int_{RG}^{\;}{t}}$

where RG is the regeneration time, Qc2 _(ini) and Qc2 are the flow values of the second component calculated respectively at a reference time and during the last calculation, Qigec_(ini) and Qigec are the flow values of the fuel quantity to be injected into the exhaust gas calculated respectively at a reference time and during the last calculation. The reference time values can correspond with previously stored values and can be read when the vehicle starts. This indicator I is based on the integral part of the closed control loop. The higher the indicator value, the poorer the open control loop is regulated. The value of the correction factor can be based on the indicator I.

As a general rule, the multiplication factor Kc is between 0.5 and 1.5 or ±50% of the nominal value. In practice, during tests, the effective range is between 0.8 and 1.2.

FIG. 3 represents in schematic manner the method for applying correction factor Kc of the first component. During step 101, indicator I is calculated as a function of values Qc2 and Q_(igec). During step 102, threshold S is calculated as a function of engine parameters such as vehicle speed or engine torque. During step 103, indicator I is compared to threshold S. If indicator I exceeds threshold S, then a validation signal is generated for the correction factor. During step 104, correction factor Kc is calculated as a function of indicator I. If a validation signal of the correction factor is generated, the correction factor Kc is applied to correct the first component.

The calculation of the correction factor and the validation of its application can take place at the end of each regeneration. If the new correction factor is valid, this factor can be updated and applied for the following regeneration(s) of the particle filter. The correction factor can be stored in the non-volatile memory of control device 8. The correction factor can be updated as soon as necessary, in particular when the catalyst is replaced. When the catalyst is replaced by a new catalyst, the correction factor must be modified in order to avoid overconsumption or excessively high exhaust temperature.

Advantageously, a device 82 modifies the flow command of the diesel injector in function of significant saturations of the richness of the gas in the exhaust line 1. The fuel flow command can be saturated before being submitted to injector 3. A more precise regulation is obtained by taking into consideration the saturations in the open control loop.

These saturations are derived mainly from the estimated oxygen concentration in the exhaust line 1. In fact, the quantity of fuel injected into the exhaust is limited by the reduction capability of catalyst 4, which depends on the available quantity of oxygen. 

1. A method for regulating the temperature of a particle filter in an exhaust line of an engine during a regeneration phase of the particle filter, by injecting fuel into exhaust gas flowing through the exhaust line, comprising the steps of: measuring the temperature at the particle filter; determining a quantity of fuel to be injected in the exhaust gas (Qigec), the quantity including a first component (Qc1 c) determined through the intermediary of an open control loop not taking into account the measured temperature, and a second component (Qc2) determined through the intermediary of a closed control loop taking into account the measured temperature; calculating a correction factor (Kc) of the first component as a function of the amplitude of the second component in comparison with the calculated quantity of fuel, and applying the correction factor in the open control loop.
 2. The method according to claim 1, further comprising the steps of calculating an indicator (I) representative of the amplitude of the second component (Qc2) in comparison with the quantity of injected fuel (Q_(igec)), and applying the correction factor of the first component in the open control loop when the indicator exceeds a predetermined threshold (S).
 3. The method according to claim 2, wherein said threshold (S) is calculated as a function of at least one operating parameter of the engine.
 4. The method according to claim 2, wherein the correction factor (Kc) of the first component is only applied in the open control loop when several successive calculated values of the indicator (I) exceed said threshold (S).
 5. The method according to claim 2, wherein the indicator I is calculated with the following equation: $I = \frac{\int_{RG}^{\;}{\left( {\frac{{Qc}\; 2}{{{{Qc}\; 2}} + Q_{IGEC}} - \frac{{Qc}\; 2_{ini}}{{{{Qc}\; 2}}_{ini} + Q_{{IGEC}_{ini}}}} \right)\ {t}}}{\int_{RG}^{\;}{t}}$ where RG is the regeneration time, Qc2 _(ini) and Qc2 are the flow values of the second component calculated respectively at the a reference time and during the calculation in progress, and Qigec_(ini) and Qigec are the flow values of the fuel quantity to be injected in the exhaust gas calculated respectively at the reference time and during the calculation in progress.
 6. The method according to claim 1, further comprising the step of determining an exhaust gas flow and an exhaust gas temperature upstream of an oxidizing catalyst installed upstream of the particle filter, wherein the open loop control is based on a model estimating the temperature at the particle filter as a function of the exhaust gas flow, the exhaust gas temperature, and as a function of the quantity of fuel to be injected (Qigec) in the exhaust gas.
 7. The method according to claim 1, further comprising the steps of detecting an engine dysfunction and maintaining the applied correction factor when the dysfunction is detected.
 8. The method according to claim 1, wherein the closed control loop comprises an integral proportional regulator.
 9. An automotive vehicle equipped with an exhaust line comprising a particle filter, a fuel injection device in the exhaust line upstream of the particle filter; a measuring device for measuring the temperature (T5) at the particle filter; a device for calculating the quantity of fuel to be injected in the exhaust gas in order to regulate the temperature (T5) at the particle filter, including an open control loop not taking into account the measured temperature and determining a first component of said fuel quantity (Qc1 c), and including a closed control loop taking into account the measured temperature and determining the second component (Qc2) of said fuel quantity; wherein the calculation device of the fuel quantity to be injected determines a correction factor (Kc) of the first component and application of this correction factor in the open control loop in function of the amplitude of the second component in comparison with the determined quantity of fuel to be injected. 